Static shadows

[BearishSun]

Objects and lights can be defined as static, but these properties are currently not used by the shadowing system. Instead shadows are re-rendered every frame, which can be prohibitively expensive. When generating shadow maps for static objects and lights, it would be best to group such static objects into a shadow map of their own, which remains static throughout the light's lifetime. All other objects should be rendered into a separate shadow map which is updated per-frame.